1. Field of the Invention
The present invention relates to devices for preventing evaporation of liquefied gas in a low-temperature generator using liquefied gas to cool an EDS detector (Energy Dispersive Spectrometer type X-ray detector) that allows electron microscopes to have the element analysis function.
2. Description of the Prior Art
Conventional electron microscopes have such an arrangement that the EDS detector is cooled with liquid nitrogen so as to enhance their measurement accuracy. In such an electron microscope, conventionally, there is provided a cold finger that is coupled with and drawn from the bottom wall of a reservoir in which liquid nitrogen is stored, and an EDS detector is mounted to the cold finger, thereby allowing the EDS detector to be held in a cryogenically low temperature state with the use of liquid nitrogen.
The EDS detector used in such a type of apparatus is required to keep its cooling temperature within a certain range once the detector has been cooled. The liquid nitrogen used to cool the EDS detector, however, is subject to some dissipation out of its reservoir due to evaporation. This compels an operator to frequently refill the liquefied gas reservoir with liquid nitrogen in order to make up for dissipated liquid nitrogen.
Disadvantageously, since an electron microscope incorporating an EDS detector restricts the floor height at which the liquefied gas reservoir for cooling the EDS detector is disposed relative to the irradiation axis thereof, the liquefied gas supply port opening at the upper portion of the reservoir has a height from the floor, for example, as high as 1.5 m. As a result, it would be laborious work for the operator to refill the liquid nitrogen reservoir with liquid nitrogen using a supply vessel such as a Dewar vessel.
The present invention has been accomplished in view of the foregoing problems and therefore it is the primary object of the invention to provide devices for preventing evaporation of liquefied gas in a liquefied gas reservoir which can dispense with the resupply of liquefied gas over a long time period.